Pulse transmission system



June 7, 1949. G. D. HULST, JR

PULSE TRANSMISSION SYSTEM Filedv July s, i945 3 Sheets-Sheet 1 o o S q n any? 0. Haw? c//a INVENTOR ATTORNEY AAAA vvv G. D. HULST, JR

PULSE TRANSMISSION SYSTEM AA Y J AYAYAYAV June 7, 1.949.

Filed July 5, '1943 1 7 mws. v. .n 2% .M C 5 :s' Smets-sheet s l l l I l l l l l l l l Il SANs-.MW H z N CCF Www/7W waw rv mm LI., N r x 5? a G. D. HULST, JR

PULSE TRANSMISSION SYSTEM -A l... 'v vvv LA; VVV

June 7, 1949.v

Filed July 5, 1943 Patented June 7, 1949 George D. Hulst, Jr., Millburn, N. J., assigner to ,Radin Corporation of America, a corporation of Delaware Application July 3, 1943,y Serial No. 493.388

17 Claims. (Cl. 25017) The present invention relates to. apparatus for transmitting pulses of energyhaving certain desired Vphaserelations.and intensities, in order to simulate conditions at a receiver designed to receive pulses from diierent remotely located transmitters. Thesystem of the invention as a whole is particularly applicable to training .personnel in the iield of navigation.

In the field' of 'long range navigation, it is important for a ship atsea or anairplane to be able to determine vits lprecise location irrespective of atmospheric conditions. In thecase of an airplane flying inthe 'dark or in inclement weather, itis important forwthepilot to .know his exact position at allztimes. With this end in view, it 'has been proposed to set up differently located pairs ofradio .transmitters and .for 'these transmitters to send outjpulses of radio frequency energy. .'Ihe radio transmitters of each pair would be geographically spaced from Aeachother at least several-milesapart, and would transmit, at different intervals, .periodically recurring pulses of the same carrier frequency and of the vsame repetition rate. Diierent pairs of radio transmitters would be located at diiierent points and would have slightly 'different pulse .repetition rates. Such a proposed .system is presently. usedior military purposes and is known asthe LRN system, the letters LRN. being the abbreviation of the expressionlongsrange navigation.

'The methody of operation of the'LRN system maybe better"'understood by referring to Fig. 1 f the accompanying drawing, wherein stations Ifand'Z represent one pair of radio pulse transmitters 'and stations 3 and 4 represent another pair of radio pulse transmitters. Transmitters I and =2 are spaced apart 'from each other by at least severalmilesylet us lsay ilfteen miles, while transmitters f3 and '4 are similarly spaced apart from each lvother, although it should be under-v stood that it 'is notnecessary `'that the stations of each .pair have the same lgeographic spacing as that-of'ranother pair. Transmitters I and 2 are remotely .located withy respect to transmitters Il and 4. preferably by` afdistanceappreciably great-a er than rthe .distance between the :stations of reach pair.A '..Stationsl .and 2 yof one pair radiate Ashort pulses of the. same .radio carrier `frequency and of the same repetitionA rate, although at slightly different times. For example, stations I and 2 may veach radiate pulses of about 40 microseconds duration having aA carrier o'f '1.95 megacycles, .these pulses recurring at a rate of 'twenty-five cycles per second. "The time'interval between the pulses radiated from "thev twostati'ons of each pair should be shorter than the time interval bei tween periodically Arecurring pulses. Thus, if the time interval between pulses from each station I or 2 is 4about 40,000 microseconds, then the'time interval between the pulses from the two "stations of each pair might ybe 15,000 microseconds. The repetition rate of the pulses from radio-stations 3 and 4 differs slightly from that of stations l and V2 and might be '251/16 pulses per second'fal though the carrier frequencies of the pulses' from the diierent pairs of stations may be the same (1.95 megacycles assumed above) or slightlydif ferent. The difference inthe repetition Yrate of the pulses from the different pairs of `stations is sulicient for an observeren a ship or airplane to distinguish between the pairs of stations.

y The curved lines A, B, C, D of Ysubstantially `hyperbolic shape, located between radio transmit ting stations I and 2, are Vseveral of many Vloci alongany one of which there is la fixed difference in distance between the two stations of vthis one pair. Similarly, curved lines A','B, C and D",'located between radio pulse transmitters 3 4and l. are several of many loci along any one of which there is a fixed diner'ence in distance between the two stations 3 and 4. The straight line E between stations I and '2, and the straight line E between stations 3 and 4 are lines on all points of which the ldistance between the stations of the respec tive pairs is the same.

An observer on a ship or plane Jdesiring to'determine his position in accordance lwiththe above long range navigation (LRN) system, is vsupplied with a map showing the location ofthe 1diierent pairs of pulsetransmittingstations I, 2: y3, Bete. and also the loci, and is also supplied with a rel ceiver which can be tuned to alternately receive the pulses radiated from the different pairs' of stations. yThis receiver is equipped with circuits for Vcalculating the time required for the pulses from the stations of a pair to travel to the ree ceiver, and converting andswiftly registering or` indicating 'this time. By tuning thev receiver u y receive the pulses of aparticular repetition ratei from one pair of transmitting stations, let us say I and 2, the observer determines the difference intime it takes for the radiated pulses from ythe two stations of this pair Vto `reach his receiver. This time -dierence 1s proportional to the 4distance diierenc'e from the observer to thelpulse transmitters and thus ythe'oizvserver learns that heis on a particular-positionof a particular locus, let us say curve C, but he may not know his exact position on 'this locus. "Then, by tuning his refceiver to the 'repetition-rate of another 'pair' oi' radio pulse transmitting stations, let us say 3 and 4, he determines the difference in time it takes for the pulses radiated from stations 3 and 4 to reach his receiver, and from this time difference he may learn that he is on locus A. Since loci C and A intersect at only one point P, the observer then knows his exact position on the map. In this way, the observer knows at all times the direction in which he is traveling and his exact position, and if he is in a bomber plane he will know when he is over the target.

In such navigation systems, the pulses from the different transmitting stations of each pair do not always arrive at the receiver with the same intensity, due to fading and atmospheric conditions. The present invention involves apparatus designed to simulate the various conditions of reception at a receiver designed for use in such a long range navigation system, and its primary purpose is to train personnel in an understanding of the long range navigation system described above.

One feature of the present invention comprises the circuit apparatus for producing a series of pulses of different amplitudes or intensities.

A more detailed description of the invention follows in conjunction with a drawing, wherein:

Fig. 1 illustrates a series of curves given to explain the operation of a long range navigation system;

Fig. 2 illustrates in outline form an embodiment of -the invention;

Fig. 3 illustrates a series of curves of different wave forms and their time relations produced by the timing unit employed in the present invention; and

Figs. 4a and 4b, taken together, illustrate the circuit details of Fig. 2.

Referring to Fig. 2 in more detail, there is shown a timing unit l supplying over leads l, 2 and 3 wave forms a, b and c, respectively. These wave forms are shown in more detail in Fig. 3. Wave form a comprises la series of non-overlapping pulses A and B which periodically recur at the same repetition rate, for example, twenty-five times per second. It should be noted that there is a small fixed time interval t between the pulses B and A and that this time interval is shorter than the time interval between sequentially recurring pulses A, A or between sequentially recurring pulses B, B. The timing unit also produces wave forms b, .c whose pulses are of opposite polarity relative to each other. The pulses of wave forms b and c are square in form, of equal length and amplitude, and equally spaced. They may have I:

the same or a slightly diierent amplitude from the pulses of wave form a. It should be noted that the square wave pulses of form b lead by a small fixed time interval the pulses A of wave form a, and that the square pulses of wave form c .lead by a small fixed amount the pulses B of curve a. The phase relations of these wave forms are adjustable in the timing apparatus. The apparatus in the timing unit |00 which produces wave forms a, b, c includes suitable means for synchronizing or locking-in the various circuits which produce the different wave forms, in order that the phase relation shown in Fig. 3 m-ay be obtained. No claim is made to the timing unit per se in the present invention, since such apparatus is known rin the art and used in the receiver of the long range navigation system described above.

The wave form a of the timing unit is supplied over lead l to a diferentiator circuit I 0| which lili impedance.

converts the pulses in lead I to the peaked wave form represented by d. The peaked wave form d is then impressed upon the clipper amplifier T1 which converts the positive and negative impulses of wave form d to negative impulses e. The output of the clipper amplifier T1 is then impressed upon a clipper amplifier T6 which converts the wave form e to the wave form f. The pulses oi wave form f are shorter in duration than the pulses of wave form a. The output of clipper amplifier T6 is then impressed upon an impedance transformer tube T5 (sometimes referred to as a cathode follower) which provides an output of wave form g of substantially the same form as wave form i. The input to the impedance transformer tube is of high impedance, while the output taken from the cathode of the tube is of low Wave form g is used to key a suitable radio frequency oscillator T4 which is pulsed to produce output pulses of radio frequency oscillations shown by wave form h. The output oi the pulsed oscillator T4 is then impressed on a differential-pulse-amplitude-control amplifier T3, upon which is also imprsssed the output of impedance transformer tube or cathode follower T8.

At this time `it should be noted that the impedance transformer T8 has impressed thereon the the output of a mixer |02, the latter in turn having supplied thereto pulses o f wave forms b and c from the timing unit |08 over leads 2 and 3, respectively. The mixer EQ2 serves to increase the amplitude of either one of the wave forms b or c with respect to the other so as to supply an output wave form which can vary in shape vanywhere from that of b to that of c. By way of analogy,

the mixer |32 can be compared to a faucet to which hot and cold water is supplied over separate conduits. By suitable adjustment of the faucet, the outlet may be made to supply more cold water or more hot water.

The impedance transformer T8 merely serves to couple the connection from the mixer HB2 which is at a high impedance to the connection to the unit T3 which is at a low impedance. The differential-pulse-amplitude-control amplifier T3 supplies an output having either one of the three wave forms J, K or m, depending upon the input supplied thereto by the mixer circuit m2. Thus, if the mixer circuit |02 minimizes the amplitude of the square pulses of wave form b with respect to the amplitude of the square pulse from wave form c, the output from unit T3 will have a wave form shown by J. On the other hand, if the amplitude of the square pulses of wave form c is increased by the mixer with respect to the arnplitude of the square pulses of wave form b, then the output from the unit T3 will have a wave form shown by K. If the mixer |02, however, is adjusted so that the wave forms b and c impressed thereon compensate or neutralize each other in the mixer, then the output of the mixer will be a straight line, in which case the unit T3 will supply a wave form of the type shown by m. It should be noted that the pulses of radio frequency energy in the output of unit T3, which may be of either of the three forms J, K or m, have a time appearance which is identical with or registers with the time appearance of the pulse of wave form a in lead l connected to the output of the timing unit.

The output of unit T3 is impressed upon the gain control amplifier T2 which serves to amplify the output of unit T3 and in turn impresses the amplified pulses of radio frequency energy upon y the power amplier Tl. The output of the power'.

e from clipper ampliiier T1 is impressed upon the The foutputl'diA`r clipper mplierf T1! :will have 'fthewai/e"ferrifflandivill -impressedupon tne'ieridf6fitheifimpedance=transformer tube or cathode?"follwrllif` fsiiilpeiiance transformer'tuloe Lissonietimes" alled a'l cathode 'iclu lower fbeeaus'eforftliefac at' ioutput f'istaken 'frciiirtneicathcdegeritliei-t be. frupe'rt merely serves tof'couple fthefliigihfimpedance i input ci 'its' ridfcircuitt' lofwfirnpedancecutput fromits cathode 'fcir'cu heipuises tlrecathcde ecirelut/rftherimp ance-tr nsiorm "ISfarerepresented iep-wave form pifessedfonthe second 'iM-fierpulsing"l "'Yfr'he "ill" T types-andan -udesffanfcscillatoryicir uitzccmprising an inductance L, a condenser C, and 'ashfuzit dampingtresistor R.'f`iI-he-inductarice L is adjusted Evin-leans 'of fa suitaieuronplug'. Oscillator 'T-'l is-'orlrfallr biase" oicuto'ifinfthe :absence of inr'ent'passing/condition'"by-"'tliefi-mpulses of wave rorrnfprappliedjtc 1a' screen irgfrid *from "the impedance ransfcrni""'T-5.` Tneoutputfircm the @sciiiilses" dfrad'iofrequency energy 'Wave-formhftake-af'littitlmetb build up and also hal/cia' 1'Sii'lslll-idecayy time, a'ut #are controllable by the design of the oscillator within certain limits. bThe' biifupiiiinefsfdohtrlled' b'yfth'e' transconductanee esthetische-YT@ and *the gain fcf ine-cs-A 'cfll-'ltei 'nfy ch'sldered as 'an -'ainplien While the d'eca'y'tiiie' is'icnt'rolldl:byfthe'timing of the timefcii-'ciuit-f*'ThecathodeJ bias 'provided by resister Rlfas's'uresa curreritcutoi condition 'dur- .ing-1 thefalos'ence "off input pulses to the screen gidff itubei-T. "The"pulses of 'radio frequency V'energy initiiewavefformfin 1the output of the oscillator-*areimpressed =upon=-the "control grid ci the ldifferentialpulse=anrip1itude@control emplia rltub''IIB.

'ine fidi-fierentiallpulseeamplitude:control empli'e'r 'animas-#impressed upon its' scatlicde the output of the impedance'transformer T3. Tube 'lislha's impressed updh'fitsrgrid'ftheroutput of the .x'rilina'r'Iltil-'2k through raiiibioclilng l-acudenser Cl. Mixer 102, iniefifetp'cnsistsof faresistor to Whose opposite;-terminalsareicrinccted leads 2 and '3, Ain A turniextndin'gvto the-rtiming'furiitfflfen. As mentionedfabovenedrznasimpressedftherecnsuuare ipiilsesioiiftheif-vvaveirorm so ytvhil'esl'esd 'e3 .nasuini ylciased 'to the cur- These 1pulses oi' Cil pressed:therednisuuarexpulses:oirlihewavmform Avta'p' On' th mixen :3112 which: :connects 'to the impedance' transformer Taxathnoughd condenser CI serves `to1p1:cmide'arxy suitable adiustrrrentver the .Jen'gth .of .l athes::resistance.uconstitutingr ithe mixer.` :Iftlie-'Jtelp iisfia'tsits uplfrmostiteminail, square pulses :etliche wavezsfornifrlriwilluce; 'passed n t0 Ithetimbedan'oetriisformeif: .iandi their itc the-iereritial'transformer-without'iiiminuticn ofintensity, whileisduare'puises of'theifxuaveifonm c will befccnsiderablyidecreased iniintensity'for amplitudecand fhavevncfeiect thecoutp'ut cisne impedance transiormcrvTB. y":tJonversely;li'fthetap on ithc mixer i' m2 'is*infitstlcwermostigiposition;the square" pulses of: wave iormc .will bespasse'd en' so theinipedance `transionmer @stand then tozithe unit-'T3 .Witlfiout change in armel-itukie,` ihii'ethe square pulses'of Wave fformib: will .be consistera-bly decreased in amplitude andsintensity-fand hai/tedio effect on .the Uutputfapplied 1to11-unit:?l%3.i f tap lon lthe @mixer is." exactly? in: the' .uente mine square pulses 'oiwaxe :formioaand :cmiiiol'rare of 'opposite .polarityiwill cancellcr neutralisesea'ch other in effect, fand' no; -:pulse :will be :passe-ttx en' itu thecat'lriodefof` tube' Tiromz'theimpedance ytre-ns'- former T8. It will thus be seenthat'thesrelatiue amplitudes cf the `.square pulses corresponding 'to waveforms ilianlzfc in the foutput aof'the initier |02 depends upon theapneclse Spositicmfof fthe tap on the mixer resistor.; :"lIhe-1uutput'r'uftulee yu'f-il comprise rad-io'rfrequency pulses'shavingzeither 'oi the *three wave fermsslfl or fm, dependingzupcn thefposition 'of ftlrettap on :the'smixs'nl'i B2. The gain'control `ampliierff iserves-"itc fthe pulses .impressed :onfit's control gri'difrdmfzthef output of the differential-pulse-ainplitudeecontrl ampliiier T3. Assuming that the-rtuloe'im'fhappens, `iat 'one particular :tmorn'enm 'to *be passing pulses df the WavefformK, fthenztheoutput 'oi'tlie gaincontrolfampl'ier T2 mayhai/eethe Waveform n, the latterv slflowing"bycciripa'risonUVA ithizthe waveform 'Kthe 'gain :providedvby thetupeflt.

The f'output ffromfitheigainzcontrol'iampiiiiervlt? is supplied to the apoweriamplrirfml,"which*in turn supplies the fampliedpulses of radio irequency energy to anfsuitablefantennaANTI: suitable ypovverl supply" uriit `is shown 'in 'bcxfPffor supplying positive rpclarizirrg: 'potentials rto". fthe electrodes of ythe various tube` 'eircuitsieind :for supplying heating current to the laments @fche diierenttubes. In .one fembodimentsucccssfully `'constructef'cl and "tried Aout Ain practiceptheiifcuit 'of 'Figs '4a" and 4b was constitutedras foliows: Thefcondenser Il) andresistor lil `ofi the2dilerentiatury circuit had respective values `Aofc-250::gultf'and' f120g000" ohms. Tube f'l was 'anLRCi6SJ'itubcL iTife .twoitriode's T5 and T6 formed one'ftube Within atsinglerem velope'and yWasaii RCA"i6Sl2.7.Ci'I"tulue. 'llfie'soscillator tube T4'Wa's Aan fRCAQGSKVIritu-be, and pro` duced oscillations fofl;'1;95 -megacycles' lThe shunt resistor R of :the 'oscillators/'as' 11120;"0001rhms, While the.y condenser' C :'o'fith'e "oscillator was *100 mit having zero 'drift. "ThetubesTS and VT2 were each`.RCA GSK? tubes. "Thep'ower" amplifier' T was an RCA GVGGTftube'g'andthe twofcondensers connected toits'outputwvere 7Aeach of v25 upf-fand had'zerofdrift. Theantenniwas oifthe telescopic rod type 'which mould-be iextende'd'tc a length of 48 in-ches. With"theiantennatexterided "tol'its fullk length of 4'8?inchespitiradiatedsa tdield 'of-approximately 10,000remicrcvfolts perimeterr at a'distance of 'thirtyffeetfinanyidirectioni L The'-"fre'` quency-of .the outputiwas @adjustable rbym'eansof ascrewdriver IQ'ictin'glenstheirorr'iplug ic'l 125 of the oscillator to provide a tuning range between 1780 and 2080 kilocycles. The amplitude of either of the two output pulses from the antenna corresponding in time relation to the two pulses A and B of wave form a could be attenuated individually and continuously by means of the mixer to less than 1/100 of the other pulses (40 decibels). When the tap on the mixer controlled by a knob was set at its center position, the amplitudes of both pulses from the antenna were the same. The time duration of each output pulse from the antenna was about 35 microseconds, the build up time being about 8 microseconds, the fiat top or constant amplitude time being about l2 microseconds, while the dec-ay time was about 15 microseconds. The time interval between adjacent pulses of each series A :or each series B was of the order of 40,000 microseconds, while the time interval between pulses A and B was of the order of 15,000 microseconds. The output of both series of pulses was continuously variable over a range of 100 to 1, by means of a knob, and this action was completely separate from the action of the knob controlling the tap on the mixer, for which reason it was possible to simulate a wide variety of eld conditions.

By using two sets of training apparatus, each of the type shown in Fig. l or Fig. 3, it is possible to simulate the conditions at a receiver designed to receive pulses from two pairs of geographically spaced radio pulse transmitters, the transmitters of each pair transmitting short pulses of radio frequency energy of the same repetition rate but spaced apart in time, and the two pairs having slightly diierent pulse repetition rates.

What is claimed is:

1. In combination, an oscillator of radio frequency energy normally biased to cut-oil?, a circuit for impressing upon said oscillator two series of unidirectional current pulses to thereby cause said oscillator to produce two corresponding series of pulses of radio frequency energy, a utilization device, an amplifier between said oscillator and said utilization device, and means coupled to said vamplifier for causing the same to change the relative amplitude of one of said series of pulses of radio frequency energy relative to the amplitude of the other series of pulses of radio frequency energy.

2. In combination, an oscillator of radio frequency energy normally biased to cut-off, a circuit for impressing upon said oscillator two series of unidirectional current pulses to thereby cause said oscillator to produce two corresponding series of pulses of radio frequency energy, a utilization device, rst and second ampliers in cascade coupling said oscillator to said utilization device, and means coupled to said first amplifier for changing the relative amplitudes of said two series of pulses of radio frequency energy.

3. In combination, an oscillator of radio frequency energy conditioned to be normally nonconductive, a circuit for impressing upon an electrode of said oscillator two series of unidirectional current pulses to thereby cause said oscillator to produce two correspondingly positioned series of pulses of radio frequency energy, a utilization device, a vacuum tube coupling the output of said oscillator to said utilization device, and means for applying to an electrode of said vacuum tube other unidirectional current pulses of relatively different time duration than said first unidirectional pulses to thereby cause said vacuum tube to change the relative amplitudes of the two series of pulses of radio frequency energy passed thereby.

4. In combination, an oscillator of radio frequency energy conditioned to be normally non.

conductive, a circuit for impressing upon an electrode of said oscillator two series of unidirectional current pulses of the same repetition rate but displaced from one another in time. to thereby cause said oscillator to produce two correspondingly positioned series of pulses of radio frequency energy, a utilization device, a vacuum tube coupling the output of said oscillator to said utilization device, and means for applying to an electrode of said vacuum tube other unidirectional current pulses of relatively different time duration than said first unidirectional pulses but synchronized with respect to said first unidirectional pulses to thereby cause said vacuum tube to change the relative amplitudes of the two series of pulses of radio frequency energy passed thereby.

5. In combination, -an oscillator of radio frequency energy conditioned to be normally nonconductive, a circuit for impressing upon an electrode of said oscillator two series of unidirectional current pulses of the same repetition rate but displaced from one another in time to thereby cause said oscillator to produce two correspondingly positioned series of pulses of radio frequency energy, a utilization device, a vacuum tube having a control electrode coupled to the output of said oscillator and an output electrode coupled to said utilization device, and means for applying to the cathode of said vacuum tube other unidirectional current pulses of relatively different time duration than said first unidirectional pulses but synchronized with respect to said iirst unidirectional pulses, to thereby cause said vacuum tube to change the relative amplitudes of the two series of pulses of radio frequency energy passed thereby.

6. The method of operating electrical apparatus which includes generating a multiplicity of spaced pulses of radio frequency energy of the same amplitude, producing a series of unidirectional pulses independently of said pulses of radio frequency energy and which are synchronized with respect to said multiplicity of pulses of radio frequency energy, and changing the amplitudes of only certain ones of said multiplicity of pulses of radio frequency energy as a function of the amplitude of said series of unidirectional pulses.

'1. A signaling system having an oscillator of radio frequency energy, said oscillator having as a part thereof a control element for determining whether or not said oscillator produces oscillations. for impressing upon said control element of said oscillator two time spaced series f of pulses of substantially uniform amplitude and duration and of the same repetition rate, to thereby cause said oscillator to produce two correspondingly positioned series of pulses of radio frequency energy, and means synchronized with respect to said two series of pulses for changing the amplitude of one series of pulses of radio frequency energy relative to that of the other series of radio frequency energy.

8. A pulse generating system having means for rst producing two series of pulses of uniform amplitude and duration and having the same repetition rate but diiferently phased in point of time, the duration of each pulse being short compared to the time interval between pulses, the spacing between a pulse of one series and the anarco:

. 9` adjacent pulsef'of t''ie'ot erseriesv being shorter than..the;lspacing between ,ad-jacent pulses of any onelseries,.and means synchronized with respect to-tsaid. twof; series of pulses-.sion subsequently changing the. relative amplitudeaof saiditwo lseries of pulses while maintainingthe same repetitionlrateand relative phase relation.

y y9. v A pulse; transmission system.- `roi simulating the conditions at a receiver adapted to receive pulses from diierentlyloc'atedpulse transmitting stationsfcomprising means :for generating@ l two series of nonsoverlapping linidirectionalxpulses of uniform duration and of the same repetition rate, means for also generating other unidirectional pulses of the same repetition rate as said rst pulses, synchronized therewith, but displaced therefrom in point of time, an oscillator of alternating current, a circuit for impressing upon said oscillator two series of pulses representative of said first two series for causing said oscillator to produce two corresponding series of pulses of alternating current energy, a differential-pulseamplitude control tube, and circuits for impressing upon different electrodes of said control tube the pulses of alternating current energy and said other unidirectional pulses for producing two series of output pulses of alternating cur rent energy of different amplitudes.

10. A pulse transmission system for simulating the conditions at a receiver adapted to receive pulses from differently located pulse transmitting stations comprising means for generating two series of non-overlapping unidirectional pulses of uniform duration and of the same repetition rate, means for also generating other unidirectional pulses of the same repetition rate as said first pulses, synchronized therewith, but displaced therefrom in point of time, a circuit for changing amplitudes of only said last unidirectional pulses, an oscillator of alternating current, a circuit for impressing upon said oscillator two series of pulses representative of said first two series for causing said oscillator to produce two corresponding series of pulses of radio frequency energy, a differential-pulse-amplitudecontrol tube, and circuits for impressing upon different electrodes of said control tube the pulses of radio frequency energy and the changed amplitude unidirectional pulses for producing two series of non-overlapping output pulses of radio frequency energy of different amplitudes and of the same repetition rate.

11. A pulse transmission system comprising a source of periodically recurring waves, a diilerentiator coupled to said source, a clipper amplier, a connection from said diierentiator to said clipper-amplifier, whereby said amplier produces pulses whose duration is shorter than that of the periodically appearing waves of said source, a radio frequency oscillator under control of said amplier for producing pulses of radio frequency energy whose duration is shorter than the time interval between pulses, an amplitude control tube, a connection from the output of said oscillator to an electrode of said control tube, a source of pulses operating in synchronism with said first source, and a connection from said source of pulses to another electrode of said control tube, to thereby vary the amplitude of said pulses of radio frequency energy as available in the output of said control tube.

12. A pulse transmission system comprising asource of periodically recurring waves, a differentiator coupled to said source, a clipper amplifier,

ai connection" A froml 'said-Af differentiat'orto said clipper amplifier, whereby -sai-cl-amplier'iproduces pulseswho'seiduration-is shorter-than that of the periodically: appearing Waveshof said =source, a radio frequency :oscillator-undercontrol of saidl amplifier for-*prodfuciiflg-pulses` efrad'io frequency energy whose duration is shorter than the time interval'betweenpulsesuand an amplitude modulator coupled to ,the4v output .of .said radio frequency oscillator.`

13,;A pulse; transmissionisystenr:comprising` a radio frequency oscillator, saidi:oscillator'fllavingr4 as an integral part thereof a control element for determining whether or not said oscillator produces oscillations, a source of periodically recurring unidirectional current pulses coupled to said control element of said oscillator for controlling said oscillator to produce correspondingly positioned pulses of radio frequency energy of uniform duration and amplitude, and means coupled to the output of said oscillator for changing the amplitude of said pulses of radio frequency energy.

14. A pulse transmission system comprising a radio frequency oscillator, said oscillator having as an integral part thereof a control element for determining whether or not said oscillator produces oscillations, a source of periodically recurring pairs of pulses coupled to said control element of said oscillator for controlling said oscillator to produce periodically recurring pairs of correspondingly positioned pulses of radio frequency energy of uniform duration and amplitude, and means coupled to the output of said oscillator and synchronized with respect to said source for changing, by a xed amount, a characteristic of only one of the pulses of each of said pairs of radio frequency pulses.

15. The method of operating electrical apparatus which includes generating a multiplicity of pulses of radio frequency energy, producing independently of said pulses of radio frequency energy a series of unidirectional current pulses oi substantially rectangular wave form and which are synchronized with respect to said multiplicity of pulses of radio frequency energy, and changing the amplitudes of only certain ones of said multiplicity oi pulses of radio frequency energy as a function of the amplitude of said series of unidirectional pulses.

16. A signaling system having an oscillator of radio frequency energy, said oscillator having as a part thereof a control element for determining Vwhether or not said oscillator produces oscillations, means for impressing upon said control element of said oscillator two time spaced series of pulses of substantially uniform amplitude and duration and of the same repetition rate, to thereby cause said oscillator to produce two correspondingly positioned series of pulses of radio frequency energy, and means including apparatus for producing in synchronous relation to said rst pulses two series of unidirectional pulses of rectangular wave form for changing the amplitude of one series of pulses of radio frequency energy relative to that of the other series of radio frequency energy.

17. A pulse transmission system comprising a radio frequency oscillator having as part thereof `a control electrode, a source of rst and second series of periodically recurring unidirectional current pulses coupled to said electrode and controlling said oscillator to produce correspondingly 11 positioned pulses of radio frequency energy of uniform duration and amplitude, and means coupled to the output of said oscillator for changing at Will the amplitude of those pulses of radio frequency energy corresponding to one series relative to those of the other series.

GEORGE D. HULST, JR.

REFERENCES CITED The following referenlces are of record in the le of this patent:

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